According to the U.S. Environmental Protection Agency, buildings accounted for about 38.9% of the total U.S. energy consumption in 2005. Residential buildings accounted for 53.7% of the total, while commercial buildings accounted for the remaining 46.3%. In addition, buildings accounted for 72% of the total U.S. electricity consumption in 2006. 51% of this total was attributed to residential building use, with the remaining 49% to commercial buildings. While energy consumption in the U.S. manufacturing sector has declined from about 22,576 trillion BTU in 2002 to about 18,817 trillion BTU in 2010, the U.S. is still the largest global consumer of energy.
Despite efforts within the residential housing industry to introduce more energy efficient technologies such as more efficient equipment, better insulation, and more efficient windows, according to the U.S. Energy Information Administration, the total energy consumption per household in the United States continues to rise, largely due to increases in electricity demand. For example, in 1993 the total consumption of energy in homes by end-users totaled about 10.01 quadrillion BTU, with about 18.3% of that utilized for water heating, and about 4.6% for air conditioning. In 2009 residential end users consumed about 10.18 quadrillion BTU, with about 17.7% of that utilized for water heating, and about 6.2% for air conditioning.
Thus, there continues to be a significant need for methods and systems that reduce energy usage and/or provide more energy efficient systems, in residential housing, commercial buildings, and industry.